Tunable cavity resonator



Oct. 11, 1955 B. D. KUMPFER 2,720,628

TUNABLE CAVITY RESONATOR Filed Sept. 5, 1950 INVENTOR. BEVERLY D. KUMPFER BYW 77X flfforng United States PatehtO TUNABLE CAVITY RESONATOR Beverly D. Kumpfer, Spring Lake Heights, N. J., assignor to the United States of America as represented by the Secretary of the Army Application September 5, 1950, Serial No. 183,222

2 Claims. (Cl. 333-83) (Granted under Title 35, U. S. Code (1952), see. 266) The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment of any royalty thereon.

This invention relates to arrangements for tuning an electromagnetic resonator of the cavity type and more particularly to resonators applicable to microwave apparatus.

One of the objects of the present invention is to provide a cavity resonator at ultra-high frequencies having improved tuning means for controlling the frequency of the resonator.

Another object of the present invention is to provide suitable means for tuning a resonant cavity through a wide range of frequency.

It is a further objectof my invention to provide a resonant cavity having dynamically balanced tuning means.

It is a further'object of my invention to provide broad range tuning means employing rotary elements to achieve a rapid rate of tuning.

For a better understanding of the invention together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawings in which:

Fig. 1 is an oblique exploded view of a resonator embodying my invention;

Fig. 2 is a partial elevational View in section of the device shown in Fig. 1;

Fig. 3 shows another illustrative embodiment of my invention; and

Fig. 4 is an end view of the device shown in Fig. 3.

Although the invention is illustrated as it may be applied to a microwave oscillator of the magnetron type, it is to be understood that the invention is not limited thereto.

Referring now to Figs. 1 and 2, there is shown a cavity resonator 2 including cylindrical cavities 4 and 6 having mutually opposed slots linked by a slot linking channel 8 to form a hole-and-slot linking channel type resonating cavity. The surfaces of slot 8 are flat as illustrated in the drawing. Although cylindrical cavities 4 and 6 are shown as having circular end surfaces, it is to be understood that other shaped end surfaces may be used.

For tuning the resonator there are provided a pair of semi-cylindrical tuning rotors 12 and 14 made of brass or other suitable non-ferrous metal, rigidly mounted on rotatable axial shafts 16 and 18 respectively. Rotor 12 is coextensive with the cylindrical wall of cavity 4 and, similarly, rotor 14 is coextensive with the cylindrical wall of cavity 6. The diameters of said rotors are slightly less than the diameter of the cylindrical cavities 4 and 6 in which they are contained. Shaft 16 is centrally positioned within cavity 4, and extends therethrough. Similarly, shaft 18 is centrally positioned within cavity 6. It can readily be seen that, by this arrangement, the rotors are free of contact from the cavity walls. For sealing cavities 4 and 6, there are provided end plates 20 and 22 having a hollowed chamber 24 to provide electromagnetic coupling between said cavities.

7 2,720,628 Patented Oct. 11, 1955 As shown, end plates 20 and 22 are secured to resonator 2 by bolts 25, or any other suitable means.

To support shafts 16 and 18 in position, each of said end plates are provided with a pair of appropriately spaced bearings 26 and 28 through which shafts 16 and 18 are extended. Any suitable means, such as gear mechanism 30 may be used for simultaneously rotating shafts 16 and 18 from outside the resonator. To offset the possibility of excessive vibration which might occur if the tuning elements were rotated simultaneously in the same direction, it is preferable, though not required, to rotate shafts 16 and 18 in opposite directions, so that when tuning element 12 is rotated clockwise, element 14 is simultaneously rotated counter-clockwise.

To more fully explain how the invention is to be embodied in an oscillator, an interdigital type magnetron 32 is shown centrally positioned within the resonator. The interdigital type magnetron is well known in the art and does not form a part of my invention. Interdigital anode 34 and the associated cathode (not shown) are centrally positioned across slot linking channel 8 and are sealed in evacuated cylinder 36. Anode 34 is supported between upper tubular structure 38 and lower tubular structure 40, said tubular structures being integral with said anode. Each of said tubular structures include upper and lower flanges 42 and 44 sealed respectively to opposite endsof cylinder 36. Supporting structure 38 extends axially through upper threaded aperture 46 and supporting structure extends axially through lower threaded aperture 47. It can readily be seen that the operating frequency of magnetron 32 is effected by the resonant characteristics of the external resonator formed by cavities 4 and 6 and slot linking channel 8.

In order to'prevent a substantial loss of radio frequency energy, it is desirable to maintain good radio frequency contact between magnetron 32 and the walls of cavities 4 and 6 at the base of upper and lower apertures 46 and 47 respectively. For this purpose contact sleeves 48 and 50 are respectively provided in said upper and lower apertures. One end of each of said sleeves converges and is longitudinally slotted to form contact fingers 52. The converging portion of said sleeves are received in sloping flanges 54 and 56 which form the respective bases of upper and lower apertures 46 and 48.

For firmly holding contact fingers 52 in position against magnetron flanges 42 and 44, threaded bushings 53 and 60 are provided. Bushing 58 which is provided with a flanged knurled head 62, is threaded into upper aperture 46 to forcibly engage with the rim of sleeve 43, thereby providing the pressure to hold said contact fingers firmly in position. For holding contact fingers of sleeve 50 in position, bushing 60, similar in structure to bushing 58, is provided in lower aperture 48.

As indicated in Fig. 1 the resonator may be formed in several parts which are symmetrical about a transverse axis in order to facilitate the assembly of the magnetron and the resonator. Guiding pins and 77 are provided to properly align both halves of resonator 2.

As is customary in the art, magnet 66 is arranged in cooperative relationship with the magnetron to provide an axial magnetic field substantially parallel to the cathode of magnetron 32.

A suitable output connection for extracting high frequency energy from the resonator is provided by a concentric transmission line including an outer conductor 68 and an inner conductor 71 culminating in a looped portion 72 extending into the hollowed chamber 24 of end plate 20. Coupling the output in this manner reduces the tendency to introduce distortion in the electric field generated in the resonating cavity by the magnetron.

In the operation of the device described, a steady magnt'ic field is applied By means are; magnet 66. A jibtential difference between the anode and cathode of magnetron 32 may be provided in any suitable manner and is represfitedlier'e for' simplicity a Battery;

a"capacitor.v Cavities 4 and 6 correspond to the inductors,

and slot linking channel 8 corresponds to the capacitor. Using this analogy, it can readily Be seen that rotors 12 and" 14 act as permeable tuners for cavities 4 and 6. With the rotors in the relative position illustrated in Fig". 2, the low est amount of inductance is present, hence the resonator frequency is at a r'r'iaiiiriuni. 'With't'h'e rotors 180 out of the position shown in Fig. 2, the inductance .will be a maximum and mecapacitasee across slot 8 will also be a maximum. eine, this position the resonant ffe'que'ncy of the resonator is at a minimum. By rotating the elements at a predetermined rate, it can r'eadily seen that the resonator frequency can be smoothly varied from one extreme to the other.

Figs. '5 and 4 illustrate another embodiment of my invention. The same elements of Figs. 1 ands are represented by the same reference numerals. As shown in Fig. 3, semi-cylindrical rotor" plates 90 and 92 are m'omited on shafts 1 and 18 respectively at opr o'size ends of cavities 6 and 4 and are equally fsp'acedthere from. It is desirable that rater plates 90 and have V a diameter substantially greater than the diameter of said cavities. It isalso desirable that the rotor plates be free of contact with each other as they are rotated. For reasons hereinbefore stated, each pair of plates are simultaneously rotated in opposite directions by any suitable means to vary the resonant characteristics of the resonator 2.

While there has been described what is at present considered to' be are preferred Embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications" a ain within the true spirit and scope of the invention.

What is claimed is:

1'. A re'so' ato'r comprising two cylindrical resonant cavities, the cylindrical walls of each of s'aid cavities having mutually opposed circumferentially spaced aiial slots, a channel linking said slots, tuning means for-varying the resonant characteristics of said resonator comprising a rotatable member extnding within each of said resonant cavities, said rotatablemembers being coextensive with the cavity walls of said resonant cavities, means centrally positioned across said channel for applying radio frequency energy to said resonator to' establish a radio frequency field therein,- r'ne'a'ns terminating the ends of said cayiti'e's for" coupling the electromagnetic component of said frequency fieldlfrom one of said cavities to the other; and gear means coupled to said rotatable nieni bers for simultaneously rotating said rotatable members in opposite directions. I 2'; The resonator defined in claim 1 wherein said rotatable members are semi-cylindrical. 1 I

References Cited in the file of this patent UNITED STATES PATENTS 2,306,282 Samuel Dec. 2;, 1 4; 2,418,469 Hags r m Apr. 1947 2,419,173 Smith Apr. 15, 1947 2,424,496 Nelson July 22, 1947 2,436,640 7 lf redholm et a1. Feb. 24, 1948 2446,5526 McArthur Aug. 10, 1948 2,451,825 Guarrera Oct. 19, 1948 Hoglund et a1. Feb. 7, 1950 

